What makes Pokémons appear anywhere in GO? [duplicate]

You will have to travel to find pokemon spawning on their own. It's based on population density measured by Android phone usage, and the myth that keeping the app open will make them spawn near you is just that - a myth (multiple people, including myself, have kept it up for hours each day in places where none ever spawn). You can use Incense to cause a random spawn near you in 5 minute intervals, and if you walk 200meters in those 5 minutes, you may be able to cause additional random spawns. Unlike lures, these incense-spawns are not related to your area, so using incense over water will not help you catch water pokemon.